Dinosaurs are the most recognizable and talked-about group of extinct animals ever to
walk the Earth. Dinosaur means "terrible lizard", which seemed like a good name at the
time. Since then, it has been found that dinosaurs aren't lizards at all - not true
reptiles. And many dinosaurs were not "terrible" - most spent their lives eating plants
and shying away from trouble. But it is the "terrible" dinosaurs that conjure up images
of carnage - huge havoc-wrecking beasts shredding their prey with large teeth and claws.
It is these images that have both frightened and inspired generations of dinosaur
lovers worldwide.

CLASSIFICATION

When dinosaurs first appeared in the fossil record, they were easily separated into
two distinct lineages by the orientation of their hip bones. The "lizard-hipped"
(saurischian) line of dinosaurs included the herbiverous sauropods and carniverous
therapods. The "bird-hipped"' (ornithischian) dinosaurs include such well-known dinosaurs
as Stegosaurus, Triceratops, Edmontosaurus, and Maiasaura. It is not yet clear how these
ornithischians are related to the saurischians. Sauropods were herbiverous (plant-eating)
saurischians that walked on all fours. They had long necks with small heads and long,
thick tails. Examples of this group of dinosaurs include Rebbachisaurus, Diplodocus,
Brachiosaurus, and Saltasaurus. The lizard-hipped therapods are the most diverse group of
dinosaurs. Some were among the smallest known dinosaurs, while others were the largest
meat-eaters to have ever lived. They walked only on their hind legs, using their small
forelimbs mainly to hold prey. Some were toothless, while others had huge, saber-like
teeth. One of the key features of saurischian therapods is that they all had clawed feet.
Examples of this group include Allosaurus, Dromaeosaurus, Carcharodontosaurus,
Spinosaurus, Gorgosaurus, and Tyrannosaurus.

TYPES OF DINOSAURS

Tyrannosaurus rex is easily the most popular dinosaur of all. This dinosaur grew to
over 40 feet long. Although it may not have been the largest, it was one of the most
powerful carnivorous animals that ever lived. Tyrannosaurus had many cutting teeth up
to six inches long, and appears to have had keen senses. Although some people think
that Tyrannosaurus was a sluggish scavenger, most scientists believe that this dinosaur
was an active predator, with powerful hind limbs built for running and equipped with
large, sharp claws. Actual fossils of Tyrannosaurus rex are among the most collectible
dinosaur fossils in the world.

Allosaurus was the most common carnivore in the western United States during the Late
Jurassic and grew to about 40 feet long. This dinosaur had powerful hind legs that
enabled it to run with speed, and smaller forelimbs, each armed with three sharp claws.
The skull of this dinosaur contained more than seventy teeth that were about three
inches long.

Carcharodontosaurus was a Cretaceous therapod which grew to about 27 feet long. This
dinosaur had large, dagger-shaped teeth with sharp cutting edges. The forelimbs were
quite short, but armed with large claws. Carcharodontosaurus remains are usually found
in parts of Northern Africa.

Spinosaurus may have been the largest meat-eating animal ever to have walked the Earth,
measuring well over 40 feet long. This dinosaur had very long spines on its thoracic
vertebrae which may have supported a sail-like membrane. This large membrane could have
served as a heat-regulating device. Spinosaurs had a mouth full of large, cone-shaped
teeth, and was thought to prey more on fish than other dinosaurs.

Stegosaurus had short front legs and a narrow snout. The most distinguishable
characteristic of this dinosaur was a double row of thin, vertically oriented,
triangular plates along its back. These plates may have helped to control body
temperature. At the end of its tail were four tall spines, arranged in pairs and angled
towards the rear.

Triceratops was a bulky plant-eating dinosaur. The distinguishing characteristic of this
dinosaur is the presence of three long horns on the skull. The teeth were elongated
blades which were not able to crush or grind food. Triceratops probably ate fibrous
plants, such as cycad or palm fronds.

Edmontosaurus is the classic duckbilled dinosaur. They were herbivores and grew to about
forty feet in length. Each animal had hundreds of strong teeth that were connected by bony tissue.
These tooth batteries formed long grinding surfaces for crushing plants. They had thin,
leathery skin which was studded with horny bumps or tubercles.

Maisaura was one of the flat-headed hadrosaurs that grew to about thirty feet in length.
They had a long, wide face with a short, wide bill. Evidence has shown that Maisaura may
have had a "motherly" instinct and nested in colonies.

Rebbachisaurus was a huge, herbiverous dinosaur which grew to about 68 feet long. This
dinosaur had a long, tapering head and a whip-like tail. The mouth contained many
peg-like teeth, and the robust hind legs possessed large claws.

Diplodocus was one of the largest of all dinosaurs growing to 88 feet in length and
weighing almost 12 tons. The neck and tail were extremely long and the limbs were quite
slender. It had an elongated snout with nostrils on top of the head and weak, peg-like
teeth only at the front of the mouth.

Saltasaurus was a plant-eating dinosaur that grew to about 40 feet in length. It is the
first sauropod known to have had armor. The long, needle-like teeth were well suited for
nipping plants.

FACTOIDS

The "Age Of Dinosaurs" makes up the majority of the Mesozoic Era. The Mesozoic extended
from 248 to 65 million years ago. During this time, dinosaurs ruled the earth. Dinosaur
remains have been found all over the world, on every continent, even Antarctica. They
lived in swamps, forests, and even near-desert environments. Dinosaurs were probably more
like today's birds and large mammals than modern-day reptiles. Some dinosaurs could
probably run at great speed, either as predator or prey. Other dinosaurs lived in large,
structure herds which provided some protection from meat-eating dinosaurs. Dinosaurs
usually laid their eggs in nests of six or more eggs and sometimes returned to the same
nesting ground year after year. Dinosaur eggs have occasionally been found in the fossil
record, and complete dinosaur eggs are extremely sought-after by collectors. Sixty five
million years ago, dinosaurs became extinct. Dozens of theories have been put forward
as to why the dinosaurs vanished after more than 150 million years of world domination.
Not even the asteroid impact theory seems to explain the whole story. The startling
disappearance of the dinosaurs is probably the greatest unsolved mystery in the
history of paleontology.